The invention relates to an optoelectronic assembly, the components which make up this assembly, as well as to the method for making the assembly.
The assembly concerns a transmitter-receiver device, by means of which light signals can be transferred into electric signals (receiver mode), or electric signals into light signals (transmitter mode).
The object of the invention is to provide such an assembly which works with high efficiency both in the transmitter and the receiver mode and which can be produced with low expenditure. It is also the object of the invention to provide the individual components for such an assembly, which can be produced at low cost in large numbers and with high precision.
This object is solved by an assembly which consists of two separate components. One of the components comprises positioning configurations, an optical waveguide, a first mirror and a second mirror, the two mirrors lying in prolongation of the optical waveguide and the second mirror, as seen from the optical waveguide, lying behind the first mirror. The second component comprises adjustment configurations, an optical transmitter and an optical receiver, the transmitter and the receiver being arranged next to one another. The two components are precisely aligned relative to each other by means of the positioning and adjustment configurations such that the first mirror can cooperate with the optical receiver and the second mirror with the optical transmitter, so that light coupled in via the optical waveguide falls on the receiver and light generated by the transmitter is coupled into the optical waveguide.
The assembly according to the invention as well as the components according to the invention which make up the assembly, offer a series of advantages. The use of a first and a second mirror in a way interleaved, i.e. in the nature of a double mirror, makes it possible to use one and the same optical waveguide for transmission of light signals directed to the receiver and of light signals generated by the transmitter. The first mirror, which preferably has a much larger surface area than the second mirror, reflects the light which exits the optical waveguide, towards the receiver. This is done with a very high efficiency, because only a very small part of the incoming light falls on the second mirror and, thus, can not be reflected towards the receiver. Vice versa, almost the whole light that is radiated from the transmitter, is reflected by the second mirror towards the optical waveguide and is coupled into it at that place, because only a very small part of the generated light is not reflected onto the end face of the optical wave guide.
Preferably, the area of the second mirror projected into a plane perpendicular to the longitudinal axis of the optical waveguide amounts to not more than {fraction (1/10)} of the projected area of the first mirror. It is in this way that the loss of the light signals directed to the receiver can be kept to a very low level.
It is further provided for that the second mirror, in a projection into a plane perpendicular to the longitudinal axis of the optical waveguide, lies within the area of the first mirror. This design likewise serves to reduce the losses, because those surface regions are minimized which can not be utilized for transmission of light.
Preferably, it is further provided for that the first and second mirrors are parabolic mirrors. Such design results in lower losses as, for instance, plane mirrors.
According to the preferred embodiment of the invention it is provided for that the focal point of the second mirror, as seen from the optical waveguide, lies behind the focal point of the first mirror. The respective focal points are coordinated with the arrangement of the transmitter and the receiver in such a way that there is an optimum transmission.
According to the preferred embodiment it is further provided for that the component which incorporates the optical waveguide is provided with a receiving groove, having a trapezoidal cross-section, for an optical fiber, and in that the optical waveguide is an optical fiber which has a trapezoidal cross-section in the region of the component. An optical fiber having a trapezoidal cross-section can be connected with the component in a much more easy and reliable way than an optical fiber with circular cross-section. Moreover, there are only very small transmission losses.
According to the preferred embodiment it is further provided for that the receiver is provided on its active surface with a filter, which is opaque for the light radiated from the transmitter. Thus, any stray light that is not coupled in from the transmitter into the optical waveguide, but falls on the receiver, does not lead to an interference of the signal transmission, because the stray light is absorbed by the filter.
On the component equipped with the transmitter and the receiver, there are preferably provided conducting tracks for connecting the transmitter and the receiver. Such conducting tracks may, in particular, be constituted by a gold coating which forms a bondable surface. The gold coating can be applied in a simple way by galvanic deposition.
A copper layer is preferably provided underneath the gold layer, this copper layer serving for carrying off the heat loss generated by the transmitter and the receiver. To this end, the copper layer is realized with a comparably large thickness.
A separation layer made of nickel is preferably applied between the gold coating and the copper layer, which separation layer prevents any diffusion of atoms of the gold coating into the copper layer. Preferably, there is further provided on the substrate of the component a starter layer made of nickel, the copper layer being able of being galvanically deposited onto this starter layer.
The assembly can be produced by a method according to the invention which comprises the following steps: At first, by taking the shape of a negative mold, there is produced a substrate having positioning configurations and at least two mirror surfaces as well as a further substrate having adjustment configurations and at least one receptacle for an optoelectronic component. Subsequently, the two substrates are metallized in a suitable way, the metallization of the mirror surfaces serving for providing a well-reflecting double mirror, whereas the metallization of the substrate, which is provided with the receptacles for the optoelectronic component, serves for connection of these components and also for carrying off the heat loss generated by them. Then, at least one optical transmitter and at least one optical receiver are mounted on the substrate provided with the receptacle. Following this, the two substrates are placed one upon the other, they being precisely aligned relative to each other by means of the adjustment and positioning configurations. Finally, the two substrates are secured to each other.
This method makes it possible to produce the two components, which finally will make up the assembly, separate from each other. It is in this way that there can be achieved a low waste rate, because a functional check can be carried out after each intermediate step. If it happens that the component does not work, only this component has to be discarded and not the entire assembly. The two substrates may be produced by means of injection molding technique, for example. In this way, there can be obtained by formation the microstructured surface of the later components with the required high accuracy along with low production costs. The two mirrors and the transmitter as well as the receiver need not to be coordinated with each other on assembly in an expensive way, as is partly required for each individual component in prior art. Rather, an optimum constructional arrangement and alignment relative to each other is defined, which with each formed component automatically occurs due to the adjustment and positioning configurations.
According to a preferred embodiment of the method according to the invention, each substrate comprises a multitude of mirror surfaces and receptacles, respectively, the individual assemblies being subsequently severed from the two superimposed and bonded substrates. Similar to chip production, there can be produced a substrate which has a very large number of corresponding configurations. As a last production step, the substrate is sliced or cut up into a multitude of individual components, so that there are low piece costs on production.